Imidazopyridine derivatives, preparation method and pharmaceutical compositions containing same

ABSTRACT

Compounds of formula (I):  
                 
wherein: 
         R 1  represents hydrogen, halogen, alkyl, polyhaloalkyl, cyano, nitro, hydroxycarbonyl, alkoxycarbonyl, aminocarbonyl, alkylaminocarbonyl or dialkylaminocarbonyl,    R 2  represents hydrogen, alkyl, an optionally substituted aryl, optionally substituted heteroaryl, or R 20 —C(X)— wherein: 
           R 20  represents alkyl, alkoxy, amino, alkylamino, dialkylamino, optionally substituted aryl or optionally substituted heteroaryl,    X represents oxygen, sulphur, or NR 21  wherein R 21  represents hydrogen or alkyl,    
           R 3  represents hydrogen atom or alkyl,    n represents integer from  1  to 6 inclusive, 
 
the representation  
                 
its enantiomers, diastereoisomers and also addition salts thereof with a pharmaceutically acceptable acid or base, and medicinal products containing the same which are useful as AMPK activators.

The invention relates to new imidazopyridine compounds, to a process fortheir preparation and to pharmaceutical compositions containing them.

From the structural point of view, very many examples of imidazopyridinecompounds are known in the literature, especially for their therapeuticqualities. By way of example, some compounds are used in the treatmentof disorders of the central nervous system (WO 0153263), of viralinfections (WO 0100611), of allergies (EP 144101) or of cancers (WO0244156).

AMP-activated protein kinase (AMPK) is a protein kinase which isinvolved in the cell response of energy stress. The protein is activatedby an increase in the intracellular concentrations of AMP following afall in the concentration of ATP, during physical exercise, for example.

AMPK phosphorylates and modifies the activity of key enzymes ofcarbohydrate metabolism. In fact, AMPK plays an important part inlipogenesis, because it inhibits the synthesis of fatty acids and ofcholesterol by inactivating acetyl-CoA carboxylase and HMG coreductase.AMPK reduces the expression of fatty acid synthase (FAS), which controlsthe synthesis of triglycerides.

In addition, AMPK also reduces the expression of one of the key enzymesof neoglucogenesis (PEPCK), which manifests itself in inhibition of thehepatic production of glucose.

Finally, AMPK increases the utilisation of glucose by facilitating thetransport of glucose in the muscle.

All those properties combine to make AMPK a target of choice in thetreatment of diabetes and of the metabolic disorders associatedtherewith, the search for pharmacological activators of AMPK accordinglybeing of fundamental value to the treatment of those pathologies [seeWinder W W and Hardie D G: AMP-activated protein kinase, a metabolicmaster switch: possible roles in type 2 diabetes; Am. J. Physiol., 40:E1-E10, (1999) and cited references].

The Applicant has now found new imidazopyridine compounds having a novelcycloalkyl-imidazopyridine structure, conferring thereon AMPK-activatingproperties and, more precisely, anti-diabetic and anti-hyperlipidaemicproperties.

The present invention relates more especially to compounds of formula(I):

wherein:

-   -   R¹ represents a hydrogen atom, a halogen atom or an alkyl,        polyhaloalkyl, cyano, nitro, hydroxycarbonyl, alkoxycarbonyl,        aminocarbonyl, alkylaminocarbonyl or dialkylaminocarbonyl group,    -   R² represents a hydrogen atom, an alkyl group, an optionally        substituted aryl group, an optionally substituted heteroaryl        group, or a group R²⁰—C(X)— wherein:        -   R²⁰ represents an alkyl group, an alkoxy group, an amino            group, an alkylamino group, a dialkylamino group, an            optionally substituted aryl group or an optionally            substituted heteroaryl group,        -   X represents an oxygen atom, a sulphur atom, or a group NR²¹            wherein R²¹ represents a hydrogen atom or an alkyl group,    -   R³ represents a hydrogen atom or an alkyl group,    -   n represents an integer from 1 to 6 inclusive,    -   the representation        to their enantiomers, diastereoisomers and also to addition        salts thereof with a pharmaceutically acceptable acid or base,        it being understood that:    -   the term “alkyl” denotes a linear or branched hydrocarbon chain        containing from 1 to 6 carbon atoms,    -   the term “alkoxy” denotes an alkyl-oxy group in which the alkyl        chain, which is linear or branched, contains from 1 to 6 carbon        atoms,    -   the term “aryl” denotes a phenyl or biphenyl group,    -   the term “polyhaloalkyl” denotes a linear or branched carbon        chain containing from 1 to 3 carbon atoms and from 1 to 7        halogen atoms,    -   the term “heteroaryl” denotes a group having from 5 to 11 ring        members which is monocyclic or bicyclic, in which at least one        of the rings is aromatic, and which contains in the monocyclic        ring system or in the bicyclic ring system 1, 2 or 3 hetero        atoms selected from nitrogen, oxygen and sulphur, and    -   the term “optionally substituted” associated with the        expressions aryl and heteroaryl means that the groups in        question are substituted by one or two identical or different        substituents selected from halogen atoms and the groups alkyl,        alkoxy, polyhaloalkyl, hydroxy, cyano, nitro, amino (optionally        substituted by one or two alkyl groups) and —C(O)R_(d) wherein        R_(d) represents a group selected from hydroxy, alkoxy and        amino, it being understood that the heteroaryl group may also be        substituted by an oxo group on the non-aromatic moiety of the        heteroaryl.

Among the pharmaceutically acceptable acids there may be mentioned,without implying any limitation, hydrochloric acid, hydrobromic acid,sulphuric acid, phosphonic acid, acetic acid, trifluoroacetic acid,lactic acid, pyruvic acid, malonic acid, succinic acid, glutaric acid,fumaric acid, tartaric acid, maleic acid, citric acid, ascorbic acid,methanesulphonic acid, camphoric acid etc.

Among the pharmaceutically acceptable bases there may be mentioned,without implying any limitation, sodium hydroxide, potassium hydroxide,triethylamine etc.

The preferred group represented by

An advantageous embodiment of the invention relates to compounds whereinR¹ represents a hydrogen atom.

Preferred compounds of the invention are those wherein R² represents ahydrogen atom or a group R²⁰—C(O)—.

Another advantageous embodiment relates to compounds of formula (1)wherein R³ represents a hydrogen atom.

The group R²⁰ to which preference is given in accordance with theinvention is an alkoxy group and more especially an ethoxy group.

In preferred compounds of the invention, n represents an integer 4, 5 or6 and more especially 5.

An especially advantageous embodiment of the invention relates tocompounds of formula (I) wherein R¹ represents a hydrogen atom, R²represents a hydrogen atom or a group R²⁰—C(O)— wherein R²⁰ representsan alkoxy group, and n is 4 or 5.

Among the preferred compounds of the invention there may be mentionedmore especially 3-cycloheptyl-3H-imidazo[4,5-b]pyridine-2-amine and3-cyclooctyl-3H-imidazo[4,5-b]-pyridine-2-amine.

The invention relates also to a process for the preparation of compoundsof formula (I), characterised in that there is used as starting materialthe compounds of formula (II):

wherein R¹ and n are as defined for formula (I), which compounds offormula (II) are condensed with isothiocyanate compounds (III):S═C═N—C(X)—R²⁰  (III)wherein X and R²⁰ are as defined for formula (I), to yield theintermediates of formula (IV):

wherein R¹, n, X and R²⁰ are as defined for formula (I),which compounds of formula (IV) undergo intramolecular cyclisation in abasic medium and in the presence of a suitable catalyst to yield thecompounds (I/a):

which are particular cases of the compounds of formula (I) wherein R¹,n, X and R²⁰ are as defined for formula (I),which compounds of formula (I/a) are optionally converted, in an acidmedium, into compounds of formula (I/b):

which are particular cases of the compounds of formula (I) wherein R¹and n are as defined for formula (I),in which compounds of formula (I/b) the amine function can befunctionalised in a basic medium, with the aid of an alkyl halide Alk-Z(wherein Alk represents an alkyl group and Z represents a halogen atom),to yield the compounds of formula (I/c):

which are a particular case of the compounds of formula (I) wherein R¹and n are as defined for formula (I) and Alk is as defined hereinbefore,which compounds of formulae (I/b) and (I/c) may, in a basic medium,optionally in the presence of suitable catalysts, be reacted with R²-Z′(wherein R² is as defined for formula (I) and Z′ represents anucleofugal group, such as a halogen atom or a trihaloalkyl group) toyield the compounds of formula (I),which compounds (I/a), (I/b) and (I/c) constitute the totality of thecompounds of formula (I) and:

-   -   which may, where necessary, be purified according to a        conventional purification technique,    -   which are separated, where necessary, into the stereoisomers        according to a conventional separation technique,    -   which are converted, if desired, into their addition salts with        a pharmaceutically acceptable acid or base,        it being understood that:    -   at any time considered to be appropriate in the course of the        process described above, for the requirements of synthesis the        carbonyl, amino or alkylamino group(s) of the starting        reagents (II) and (III) may be protected and then, after        condensation, deprotected,    -   the reagents (II) and (III) are prepared according to known        procedures described in the literature.

The compounds exhibit especially an excellent activity in reducingtriglyceride and blood glucose levels. Those properties justify theiruse therapeutically in the treatment and/or prophylaxis ofhyperglycaemia, dyslipidaemia and, more especially, in the treatment ofnon-insulin-dependent, type II diabetes, of obesity, of glucoseintolerance and of complications of diabetes especially in thecardiovascular area.

The activity of those compounds is also recommended for the treatmentand/or prophylaxis of other diseases including type I diabetes,hypertriglyceridaemias, metabolic syndrome, insulin resistance,dyslipidaemia in diabetics, hyperlipidaemia and hypercholesterolaemia.

The present invention relates also to pharmaceutical compositionscomprising as active ingredient at least one compound of formula (I),alone or in combination with one or more inert, non-toxic,pharmaceutically acceptable excipients or carriers.

Among the pharmaceutical compositions according to the invention theremay be mentioned more especially those that are suitable for oral,parenteral and nasal administration, tablets or dragées, sublingualtablets, gelatin capsules, lozenges, suppositories, creams, ointments,dermal gels etc.

The useful dose varies according to the age and weight of the patient,the nature and severity of the disorder and the administration route,which may be oral, nasal, rectal or parenteral. Generally, the unit doseranges from 0.1 to 500 mg per 24 hours, for treatment in from 1 to 3administrations.

The Examples that follow illustrate the invention, without limiting itin any way. The structures of the compounds described have beenconfirmed by customary spectroscopic and spectrometric techniques.

The starting materials used are known products or are prepared accordingto known procedures.

Preparation 1: N²-Cyclohexyl-2,3-pyridinediamine Step a:N-Cyclohexyl-3-nitro-2-pyridineamine

A mixture composed of 0.1 mol (15.85 g) of 2-chloro-3-nitropyridine and0.1 mol (11.50 ml) of cyclohexylamine is heated at 120° C. for 4 hoursin 250 ml of DMF in the presence of potassium carbonate (13.81 g). Thesolution is then extracted with 200 ml of ether and the organic phase iswashed three times with water. After drying over magnesium sulphate, theether is evaporated off.

Step b: N²-Cyclohexyl-2,3-pyridinediamine

800 ml of ethanol, 0.05 mol (11.06 g) of the nitrated compound preparedin the preceding Step and 3.5 g of palladium-on-carbon are introducedinto an autoclave. The mixture is heated at 60° C. for 30 minutes under50 kg of hydrogen and then stirred horizontally at ambient temperaturefor 3 hours in order to homogenise the solution. After that time, thesolution is filtered through a Büchner and then a double filter in orderto remove the final residues of palladium-on-carbon, and the ethanol isevaporated off under reduced pressure.

Preparation 2: N²-Cycloheptyl-2,3-pyridinediamine

The experimental protocol is identical with that used in Preparation 1,starting from cycloheptylamine instead of cyclohexylamine in Step a.

Preparation 3: N²-Cyclooctyl-2,3-pyridinediamine

The experimental protocol is identical with that used in Preparation 1,starting from cyclo-octylamine instead of cyclohexylamine in Step a.

EXAMPLE 1 Ethyl 3-cyclohexyl-3H-imidazo[4,5-b]pyrid-2-ylcarbamate Stepa: Ethyl{[2-(cyclohexylamino)-3-pyridyl]imino}(diethylamino)methylcarbamate

A mixture of 0.02 mol (3.82 g) of 3-amino-2-cyclohexylaminopyridine fromPreparation 1 and 0.02 mol of ethoxycarbonyl isothiocyanate is stirredin 50 ml of DMF at ambient temperature for 3 hours. The solution is thencooled to 0° C., and 0.05 mol of dipropylamine and then 0.02 mol ofmercuric chloride are added in succession. After 15 minutes, the icebath is removed and the solution is stirred at ambient temperature for 4hours. After diluting the solution with 100 ml of ethyl acetate,filtration is carried out over Celite and the solvents are evaporatedoff under reduced pressure. The resulting crude product is thenrecrystallised from acetonitrile.

Step b: Ethyl 3-cyclohexyl-3H-imidazo[4,5-b]pyrid-2-ylcarbamate

0.0048 mol of the compound prepared in the preceding Step is dissolvedin 100 ml of a solution of methanol and 15% sodium hydroxide solution(50/50). After heating the solution at reflux for 3 hours, the methanolis evaporated off. The precipitate so obtained is suction filtered,washed with water and recrystallised from acetonitrile.

Melting point: 264° C.

EXAMPLE 2 Ethyl 3-cycloheptyl-3H-imidazo[4,5-b]pyrid-2-ylcarbamate

The experimental protocol is identical with that used in Example 1,starting in Step a from 3-amino-2-cycloheptylaminopyridine fromPreparation 2 instead of 3-amino-2-cyclohexylaminopyridine.

Melting point: 177° C.

EXAMPLE 3 3-Cyclohexyl-3H-imidazo[4,5-b]pyridine-2-amine

The compound of Example 1 is added to 100 ml of a dioxane solutionsaturated with gaseous HCl, and the solution is heated at reflux for 12hours. After cooling the solution, the precipitate is suction filtered,washed with sodium bicarbonate and then recrystallised fromacetonitrile.

Melting point: 210° C.

EXAMPLE 4 3-Cycloheptyl-3H-imidazo[4,5-b]pyridine-2-amine

The experimental protocol is identical with that used in Example 3,using the compound of Example 2 as starting material.

Melting point: 210° C.

EXAMPLE 5 3-Cyclooctyl-3H-imidazo[4,5-b]pyridine-2-amine

The experimental protocol is identical with that used in Example 1,starting in Step a from 3-amino-2-cyclooctylaminopyridine of Preparation3 instead of 3-amino-2-cyclohexylaminopyridine.

Melting point: 198° C.

Pharmacological Study EXAMPLE A AMPK Activity in a Cell Model:Hepatocytes Isolated from Rats

The hepatocytes are isolated according to the technique of Berry andFriend [J. Cell Biol, 43, 506-520 (1969)]. The AMPK activity wasmeasured according to the method described by Davies el al. [Eur. J.Biochem., 186, 123-128 (1989)]. The latter involves phosphorylationstarting from [γ-³²P]-ATP of a peptide substrate (SAMS), based on thesequence surrounding the site phosphorylated by the AMPK of the ACC. Thereaction for measuring the AMPK activity ends with the deposition of analiquot of the reaction medium on a phosphocellulose paper (WhatmanP81), on which the SAMS peptide is fixed and the radioactivity of whichis measured after washing.

By way of example, the compound of Example 4 activates AMPK, after 30minutes at a concentration of 500 μM, by 312% (compared with the basevalue), whereas the same concentration of AICA riboside, used asreference, under the same conditions, activates it by 178%.

EXAMPLE B Hypolipaemic Activity

The products of the invention were tested in vivo in the obese ob/obmouse, used as a model of obesity-associated insulin resistance. By wayof example, the compound of Example 4 significantly reduces thetriglycerides at 125 mg/kg per os whereas, with metformin, the samereduction is obtained at 250 mg/kg per os.

In this model, the compounds of the invention have thus been shown to bepowerful hypolipaemic agents.

EXAMPLE C Pharmaceutical Composition

Formulation for the preparation of 1000 tablets each containing 5 mg:Compound of Example 4 5 g Hydroxypropylmethylcellulose 2 g Wheat starch10 g Lactose 100 g Magnesium stearate 3 g

1-15. (canceled) 16- A compound of formula (I):

wherein: R¹ represents hydrogen, halogen, alkyl, polyhaloalkyl, cyano,nitro, hydroxycarbonyl, alkoxycarbonyl, aminocarbonyl,alkylaminocarbonyl or dialkylaminocarbonyl, R² represents hydrogen,alkyl, optionally substituted aryl, optionally substituted heteroaryl,or R²⁰—C(X)— wherein: R²⁰ represents alkyl, alkoxy, amino, alkylamino,dialkylamino, optionally substituted aryl or optionally substitutedheteroaryl, X represents oxygen, sulphur, or NR²¹ wherein R²¹ representshydrogen or alkyl, R³ represents hydrogen or alkyl, n represents aninteger from 1 to 6 inclusive, the representation

its enantiomers, diastereoisomers and addition salts thereof with apharmaceutically acceptable acid or base, it being understood that: theterm “alkyl” denotes linear or branched hydrocarbon chain having from 1to 6 carbon atoms, the term “alkoxy” denotes an alkyl-oxy in which thealkyl chain, which is linear or branched, has from 1 to 6 carbon atoms,the term “aryl” denotes phenyl or biphenyl, the term “polyhaloalkyl”denotes a linear or branched carbon chain having from 1 to 3 carbonatoms and from 1 to 7 halogen atoms, the term “heteroaryl” denotes agroup having from 5 to 11 ring members which is monocyclic or bicyclic,in which at least one of the rings is aromatic, and which contains inthe monocyclic ring system or in the bicyclic ring system 1, 2 or 3hetero atoms selected from nitrogen, oxygen and sulphur, and theexpression “optionally substituted” associated with the expressions aryland heteroaryl means that the groups in question are substituted by oneor two identical or different substituents selected from halogen, alkyl,alkoxy, polyhaloalkyl, hydroxy, cyano, nitro, amino (optionallysubstituted by one or two alkyl groups) and —C(O)R_(d) wherein R_(d)represents a group selected from hydroxy, alkoxy and amino, it beingunderstood that the heteroaryl may also be substituted by an oxo moietyon the non-aromatic moiety of the heteroaryl. 17- A compound of claim16, wherein the representation

18- A compound of claim 16, wherein R¹ represents hydrogen. 19- Acompound of claim 16, wherein R² represents hydrogen. 20- A compound ofclaim 16, wherein R² represents a group R²⁰—C(O)—. 21- A compound ofclaim 16, wherein R³ represents hydrogen. 22- A compound of claim 16,wherein R²⁰ represents alkoxy. 23- A compound of claim 16, wherein nrepresents an integer from 4 to 6 inclusive. 24- A compound of claim 16,wherein

R¹ represents hydrogen, R² represents hydrogen or a group R²⁰—C(O)—,wherein R²⁰ represents alkoxy, and n is 4 or
 5. 25- A compound of claim16, which is 3-cycloheptyl-3H-imidazo[4,5-b]pyridine-2-amine. 26- Acompound of claim 16, which is3-cyclooctyl-3H-imidazo[4,5-b]pyridine-2-amine. 27- A pharmaceuticalcomposition useful as an AMPK activator, comprising as active principleand effective amount of a compound as claimed in claim 16, together withone or more inert, non-toxic, pharmaceutically acceptable excipients orvehicles. 28- A method for treating a living animal body, including ahuman, afflicted with a condition selected from non-insulin-dependent,type II diabetes, obesity, type I diabetes, hyperlipidaemia,hypercholesterolaemia and their cardiovascular complications, comprisingthe step of administering to the living animal body, including a human,an amount of a compound of claim 16, which is effective for alleviationof the condition. 29- A method for treating a living animal body,including a human, afflicted with a condition selected from type I andII diabetes and their cardiovascular complications, comprising the stepof administering to the living animal body, including a human, an amountof a compound of claim 16, which is effective for alleviation of thecondition. 30- A method for treating a living animal body, including ahuman, afflicted with a condition selected from type I and II diabetes,comprising the step of administering to the living animal body,including a human, an amount of a compound of claim 16, which iseffective for alleviation of the condition.